crf 250 smoking

I have an 06 crf250 that just was put back together new rings and crank and seals . starts and runs great after my son runs a practice noticed oil coming out of the air box drain, when he started it it blew a ton of smoke than stoped, this happens every moto replace the valve seals also does anyone have any idea what could cause this

Did you stagger the rings when you put it together? Seems to me that it's building up too much crankcase pressure. I think it's smoking because it's blowing the oil into the airbox through the breather hose that comes from the valve cover. I would disconnect it, plug the airbox nipple and run a straight hose from the valve cover down to where the other hoses are at. I do that on all the bikes. But, that doesn't fix the issue.

rings have been double checked, on this motor we hade to change the cases becaus of the crank cracking the cases now i used 05 cases have you ever heard of having to modifiy the cylinder for the oil squirter and do you think that may cause the problem

rings have been double checked, on this motor we hade to change the cases becaus of the crank cracking the cases now i used 05 cases have you ever heard of having to modifiy the cylinder for the oil squirter and do you think that may cause the problem

I've heard of it being done, but I've personally never done it. Moto_x2005 can probably elaborate on that part. I really don't think that's your issue regardless. It could also be the valve guides are worn pretty bad. My kids old 06 actually cracked a guide and a piece of it dropped into the cylinder and bound up the engine. It was severly worn, but I don't remember if it was blowing oil out. I know if the bike gets turned on it's side or upside down, it will blow oil out of it.

did you use pattern gaskets or genuine gaskets. i had this problem a while ago on a engine when i used pattern gaskets as one of the oil ways was missing on the centre case gasket, i changed it to a genuine one and problem was solved.

will o4 crank cases work for a 06 motor and are the gaskets the same may be i am blocking a oil port with using 06 gasket

if you had an 04 motor(cases) and wanted to run an 05+ cylinder they had to modified (cylinder skirt had to be cut to clear the oil jet) other then that your fine

do the block off kit as charlie suggested and run the hose straight to the ground, next check the trans. oil level.. is it fine? just making sure you didnt blow a right crank seal and the crank case is filling up with oil and blowing it out into the airbox.. usually when the seal goes its the tranny that fills up..

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